The present preferred embodiment relates to an arrangement and a method for inking an applicator element of an electrophotographic printer or copier. A two-component mixture comprising electrically charged toner particles and ferromagnetic carrier particles adheres to the outer surface of a roller. The two-component mixture adhering to the outer surface of the roller can be guided past an applicator element.
In known high-performance printers and high-performance copiers, it is common practice to produce a uniform layer of toner particles on an applicator element, in particular an applicator roller, and to use this layer to ink a charge image present on a photoconductor with toner. Further, it is known to ink the layer of toner particles present on the surface of the applicator element with the aid of a particle mixture comprising ferromagnetic carrier particles and electrically charged toner particles and adhering to the surface of a magnetic roller. This particle mixture is preferably mixed in a so-called mixing chamber, the toner particles being triboelectrically charged by this mixing process.
A paddle wheel is preferably used to bring the particle mixture into contact with the surface of the magnetic roller, which paddle wheel throws the particle mixture against the surface of the magnetic roller. Inside the magnetic roller, magnetic elements, preferably permanent magnets, are stationarily arranged which hold the ferromagnetic carrier particles and the toner particles adhering to the ferromagnetic carrier particles on the surface of the magnetic roller. At least part of the poles of magnetic elements are arranged close to the surface of the magnetic roller, as a result whereof accumulations of the two-component mixture build up in the area of these poles, which accumulations will have a brush-shaped orientation along the field lines of the magnetic field created by the respective magnetic element. These accumulations are also referred to as a magnetic brush.
Preferably, the stationary magnets are arranged inside the magnetic roller such that at least one magnetic element is arranged such that the magnetic brush created by this magnetic element contacts the surface of the applicator element, as a result whereof some of the electrically charged toner particles contained in the magnetic brush will adhere to the surface of the applicator element and are thus transferred to the applicator element. The separation of the electrically charged toner particles from the ferromagnetic carrier particles and the adhering of the toner particles to the surface of the applicator element is usually at least favored by a potential difference between the surface of the magnetic roller and the applicator element, which potential difference exerts a force on the electrically charged toner particles in the direction of the surface of the applicator element.
The layer thickness of the toner particle layer produced on the surface of the applicator element is primarily dependent on the amount of toner particles contained in the particle mixture and the potential difference between the surface of the magnetic roller and the surface of the applicator element. With the aid of the toner particle layer produced on the applicator element, a charge image present on the photoconductor is inked with toner and as a result thereof developed by way of direct contact of the applicator element with the charge image present on the photoconductor or by transferring toner particles across an air gap between the applicator element and the photoconductor. Such methods of image development are particularly known from U.S. Pat. No. 4,383,497. The layer thickness produced on the applicator element is decisive for the inking of the charge image on the photoconductor.
Given high process speeds, in particular in the case of high performance printers having printing rates of more than 150 sheets DIN A4 per minute, a stable and uniform toner charging and a uniform layer thickness of the toner particle layer produced on the applicator element is not safely guaranteed in each operating state. In the case of very high process speeds, too, in the prior art only the toner material that is present in the part of the magnetic brush contacting the applicator element is available for inking the applicator element. However, the height of the magnetic brush on the outer circumferential surface of the magnetic roller and the width of the magnetic brush in the circumferential direction, which both determine the volume of the magnetic brush, as well as the shape of the magnetic brush are particularly limited by the spatial dimensions of the developer station in which the applicator element and the magnetic roller are located.
Further, the mixing ratio of the two-component mixture cannot be changed arbitrarily in favor of the toner particle proportion since in the case of a supersaturation of the two-component mixture with toner particles the same are not sufficiently triboelectrically charged and the carrier particles will age more rapidly. For the problems described, the process speeds in known printer devices comprising an applicator element cannot be arbitrarily increased.
By providing several magnetic rollers for inking an applicator element the amount of toner particles provided for inking the applicator rollers could be increased. However in addition to increased costs, this would also result in an increased space requirement for the developer unit. Further, arrangements for inking and cleaning the applicator element are known in which two magnetic rollers are in contact with the surface of the applicator element. Such a device is known, for example, from the document WO 03/036393. The contents of this document are herewith incorporated into the present application by way of reference.
From the document U.S. Pat. No. 6,463,244 B2, an arrangement for inking an applicator element is known in which a magnetic roller is used for transporting a two-component mixture as well as for inking the applicator element. The magnetic roller has a stator comprising magnets as well as a magnetic roller sleeve rotating about this stator. Alternatively, the sleeve can be formed as a stator, and the magnetic elements are then arranged on a rotor.
From the document U.S. Pat. No. 4,067,295, an arrangement for the transport of magnetic electrically uncharged toner is known in which the magnetic properties of the toner are used for the transport.
From the document JP 58055941 A, an arrangement for the direct development of a charge image present on a photoconductor drum is known.
From the document U.S. Pat. No. 5,926,676, an arrangement for adjusting the height of a magnetic brush with the aid of oppositely arranged magnetic elements is known.